This invention relates to a perimetric instrument for measuring a range of a visual field of a man, and more particularly to a perimetric instrument which includes an abnormal visual field pattern analogical inferring section employing a multilayer neural network and can analogically infer an abnormal pattern of a visual field of a measurement object person and besides can automatically determine an additional target.
Measurement of a visual field is considered very important among clinical inspections of the ophthalmology and is utilized for the diagnosis of glaucoma, detached retinas, a brain injury, hysteria and so forth.
A visual field is "a range over which an eye is capable of seeing when it gazes steadily at a point", but since the sensitivity of the retina is not uniform in the range of a visual field, a visual field is accurately defined as "a sensitivity distribution of the visual sense". Perimetric instruments used for such clinical inspections include a dynamic quantitative perimetric instrument and a static quantitative perimetric instrument.
A line which interconnects different points of the retina at which the sensitivity is equal is called an equal sensitivity line isopter, and if various targets having different brightness values and sizes are moved from a periphery to the center and figures formed by interconnecting such points at which the targets are first recognized (or missed) are obtained, then various isopters can be obtained. According to a dynamic quantitative visual field, a visual field table is obtained by suitably selecting an isopter, and for example, a perimeter wherein a target is presented with various brightness values on a semicircular screen and a brightness (threshold value) at which a measurement object person begins to feel the target is found out at the individual positions and then such brightness values are indicated in a figure is a Goldmann perimeter. A measurer makes use of the figure to judge abnormality of a visual field (location at which the sensitivity is low) of the measurement object person.
A method of measuring a sensitivity of the retina with a reciprocal number to a brightness when a target is recognized at first while the brightness is raised with the position of a visual field held fixed is static quantitative visual field measurement.
Those perimetric instruments have two types including a manual type and an automatic type.
Manual measurement is a method wherein a measurer presents a target and determines a next measurement point while confirming a response to the target.
On the other hand, automatic measurement is a method wherein an order of presentation of targets is determined in advance in accordance with a program or the like and presentation is proceeded in accordance with the order. With such automatic perimeter, also static quantitative measurement by a stimulus above a threshold value can be performed readily. Static quantitative measurement by a stimulus above a threshold value is a method wherein stimulating light brighter than a threshold value is presented and it is confirmed that the stimulating light can be seen.
In order to precisely judge abnormality of a visual field, it is desirable to measure efficiently at inspection positions in accordance with symptoms. In this regard, a perimeter of the manual type has an advantage that it can measure at measuring positions in accordance with symptoms, but it has a drawback that considerable experience and attentiveness are required for a measurer such that various abnormal visual field patterns are grasped sufficiently and accordingly burdens to the measurer are very heavy. If it is assumed that the range of 360 degrees of a visual field is inspected for each 30 degrees using a Goldmann perimeter, then a target must be moved repetitively to 12 directions, and besides, in case an abnormal portion is found out, the neighborhood of the portion must be measured further particularly. Consequently, there is another drawback that very much time is required. Accordingly, there is a serious problem that not only a measurer is compelled by much labor but also a feeling of fatigue is given to a measurement object person.
With an automatic perimeter of the automatic type, burdens to a measurer are reduced because the apparatus itself presents a target automatically, but there is a problem that it cannot measure a measuring points in accordance with symptoms.
Thus, appearance of a perimetric instrument is demanded strongly which can reduce burdens to a measurer and a measurement object person by analogically inferring an abnormal visual field pattern of the measurement object person and helping the diagnosis of the measurer and further measurement points can be determined in accordance with an abnormal visual pattern obtained by such measurement.